[TRNSYS-users] Problem with Uwin value and Uframe

[Amelie Mariller]

Vous en souhaitant bonne réception, 
Amélie MARILLER
ETAMINE Nouvelles coordonnées 
6 rue du Méboud
69120 VAULX EN VELIN
Tel 04 37 45 34 20
Fax 04 37 45 41 38
 
Thank you for this remark, can you explain why the Uvalue depends on the temperature difference is it because of radiation, convection or both in the air or gas space between the panes?
Kind regards
Amelie Mariller 
-----Message d'origine-----
De : trnsys-users-bounces at engr.wisc.edu [mailto:trnsys-users-bounces at engr.wisc.edu] De la part de Matthias Rudolph
Envoyé : vendredi 2 septembre 2005 12:31
À : trnsys-users at engr.wisc.edu
Objet : AW: [TRNSYS-users] Problem with Uwin value and Uframe

Dear Amelie and Diego,

another effect that has to be taken into accout is that the u-value of the window depends on the temperature difference between the panes. At low temperature differences the u-value decreases.

kind regards,
Matthias

-----Ursprüngliche Nachricht-----
Von: trnsys-users-bounces at engr.wisc.edu [mailto:trnsys-users-bounces at engr.wisc.edu] Im Auftrag von Diego A. Arias
Gesendet: Donnerstag, 1. September 2005 23:42
An: trnsys-users at engr.wisc.edu
Betreff: Re: [TRNSYS-users] Problem with Uwin value and Uframe


Dear Amelie:

I think I have an idea of what is happening.  I would recommend looking at section 2.2.8. of the second part of Volume '6-MultizoneBuilding.pdf'.  Paraphrasing what this section explains:
- u_window = f_frame * u_frame + (1 - f_frame) * u_glass
- u_glass = (A_centr * u_centr + A_edge*u_edge) / (A_cent + A_edge)
- u_edge = c_edge,1 + c_edge,2* u_centr + c_edge,3 * u_centr2 where, u_window : u-value of the window, taking into account edge effects and frame effects.
u_glass: u-value of the window, taking into account the edge effects.
u_edge: u-value of the glazing edge of the glass.  This value is calculated by the program WINDOW4.1, and in implemented in the window library.
u_centr: center of glass u-value

Therefore, the value that you get, 2.1 W/(m².K), does not take into account the edge effects that Prebid is calculating.  I hope this helps.  Please let me know if you have additional questions.

Diego

> We have a problem about the U-value of the windows described in 
> Prebid. The value given by TRNSYS simulation does not match with the 
> one we calculate ourselves.
>
> For example, on a very basic building with only one window and no 
> solar radiation at all, when Ug=1.3 W/(m².K), Uf=23.88 kJ/(h.m².K) and 
> area of frame per window x=0.15, we calculate Uw=Ug*(1-x)+Uf/3.6*x=2.1 
> W/(m².K), and the u-win value output by Prebid is 1.81 W/(m².K).
>
> Is there an explanation to these results and how can we be sure to 
> give Prebid the right value of Uframe in ordert to get the right value 
> of u-win (here (2.1 w/(m².K) )?
>

-- 

Diego A. Arias
TRNSYS Coordinator
Solar Energy Laboratory
University of Wisconsin - Madison
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